Originally Posted by Evil Q
BG1 is worth a playthrough, if only for taking your PC from a Level 1 weakling all the way to a Level 50 god.
I did that once... exported/imported the same triple-multiclassed half-elven character for multiple playthroughs until I had reached the level cap in all 3 classes. Somewhat overkill.
Won't work though if you want to play as one of the new classes/specializations introduced in Baldurs Gate II. If you play BG2 first then BG1 will probably feel a bit dull and primitive by comparison. At least it did for me.